Study of Cables in the Distribution System: Parameters Calculation, Fault Analysis, and Configuration Optimization

Underground cables offer more advantages than overhead lines since cables are better protected and do not detract from the appearance of urban areas. In recent years, more and more electrical utilities are using cables to distribute electric power to their customers. However, the cost of installation and maintenance of underground cables is very expensive. Thus, the proper design and operation of distribution systems are crucial for economic reasons. To design and operate the distribution system properly, analysis of the underground cable system is extremely important. The objective of this dissertation is to analyze the underground cable distribution system under both normal and faulted conditions to fully understand an underground cable system. For cables to operate under normal conditions in a distribution system, two aspects must be analyzed: firstly, the parameters of different types of cables under normal operation, which include impedance matrix, power loss, and voltage drop; and secondly, the best configuration of cables in a ductbank based on the total ampacity value. When faults occur in the underground cable system, three aspects need to be analyzed: firstly, the magnetic force waveforms of cables during different types of faults; secondly, the relationship between two types of faults, namely low-impedance short-circuit fault and high impedance fault; and thirdly, the impacts of a fault on the configuration optimization. To calculate the parameters of different types of cables, a program with graphical user interface was built in MATLAB. Utilizing modeling technology, the magnetic force analysis of different types of faults was completed using COMSOL software. The impact of high impedance fault on ferroresonance was simulated in PSCAD and COMSOL. The magnetic force waveforms of cables under different faults were calculated and plotted, and the relationship between water tree and ferroresonance was observed. Then an optimization program using MATLAB and Yalmip toolbox was undertaken to find the best configuration of cables in a ductbank based on the total ampacity value. Based on the optimization results, the best configurations of cables in a ductbank under both balanced and unbalanced scenarios, even in faulted conditions, were obtained